Workspace Testing rework

[erri120]

Related to #674 and #791.

Changes:

• Reworked the GridUtils tests.
• Added WorkspaceGridState and PanelGridState to make it easier to work with the current state.
• Added IsPerfectGrid and additional checks to make sure the code does what it's supposed to do.

[codecov-commenter]

Codecov Report

Merging #809 (e098c00) into main (c9dcc7a) will increase coverage by 0.77%.
Report is 2 commits behind head on main.
The diff coverage is 69.39%.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #809      +/-   ##
==========================================
+ Coverage   60.29%   61.06%   +0.77%     
==========================================
  Files         613      615       +2     
  Lines       18641    18786     +145     
  Branches     1339     1358      +19     
==========================================
+ Hits        11239    11472     +233     
+ Misses       7054     6967      -87     
+ Partials      348      347       -1     

Flag	Coverage Δ
Linux	60.36% <69.39%> (+0.07%)	⬆️
Windows	60.26% <69.39%> (∅)
clean_environment_tests	61.04% <69.39%> (+0.75%)	⬆️
network_tests	?
networking_tests	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
...NexusMods.App.UI/WorkspaceSystem/PanelGridState.cs	100.00% <100.00%> (ø)
...UI/WorkspaceSystem/Workspace/WorkspaceViewModel.cs	0.00% <0.00%> (ø)
src/NexusMods.App.UI/WorkspaceSystem/GridUtils.cs	92.41% <78.72%> (-0.01%)	⬇️
...sMods.App.UI/WorkspaceSystem/WorkspaceGridState.cs	65.28% <65.28%> (ø)

... and 33 files with indirect coverage changes